Various liquids, often water, are used as heat transfer media in power plants. The liquid is heated to vaporize it, the vaporous fluid flows through a flow system, usually an enclosed system, and, still within the system, expands to drive a turbine or the like. Thereafter, the fluid is condensed and is cycled back to the portion of the flowpath wherein it is heated. In the case of a nuclear reactor this portion can be where it is contacted with walls heated by an intermediate heat transfer fluid which can be water or sodium, in fossil fuel plants this can be through contact of pipes which contain the fluid with hot walls, flames or hot gases created by the combustion of fossil fuel.
As a fluid, for example water, circulates through such a heat transfer system it can pick up corrosion products and deposit them throughout the system, including in the flowmeters of the system. As a result, even if each flowmeter is precisely calibrated before it is put into use in such a system the calibration is no longer accurate after a period of time. Thus, it is desirable to periodically recalibrate flowmeters. In large heat transfer systems of the nature used in power plants (wherein flow rates are generally 5.times.10.sup.6 Kg/hour or more) the most accurate method for field calibration is the radioactive sodium-24 tracer method. Carrying out this method is very expensive, however, and is generally not viable for applications outside of the nuclear industry as a radioactive materials license is required. Additionally, manufacture, transport and disposal of the radioactive sodium-24 tracer is both very expensive and very highly trained manpower intensive.
There are other calibration methods which exist using non-radioactive chemical tracers and which use chemicals dissolved in the system liquid. However, these methods have technical problems associated with them. First, chemical additives can be deleterious to materials in the system and can become concentrated in the boilers of power plants causing accelerated localized corrosion. Perhaps the best commercial chemical tracers found to date are potassium and lithium. A soluble salt or base compound must be used, however, to inject them into the flow system. The associated anion can be much more deleterious to the system than the cation tracer. Lithium is the preferred chemical tracer since it can be introduced as the base, lithium hydroxide. This can, however, impact water quality specifications for plants using ultrapure feed water.
The sensitivity and accuracy of the analysis for the tracer are the ultimate criteria for all the tracer techniques. With flow rates of 5.times.10.sup.-6 Kg/hr or greater any tracer is very highly diluted before a sample is taken for analysis. The radioactive sodium technique is the most accurate method since accurate detectability in the samples is feasible in the sub part per trillion concentration range. Because the best chemical techniques for elemental analysis are in the part per billion range, without concentration, the chemical tracer method is not sensitive enough and is therefore very subject to error. A flow element must be calibrated with errors of less than about 0.25%. Therefore, if analytical errors or sample concentration errors are greater than this, the chemical tracer method is rendered useless.
The present invention is directed to overcoming one or more of the problems as set forth above.